My 17 year old sister always gets my stuff...

The title says it all. We still live at home with my mom I’m 27 and I have a 2 year old and I am living with my mom because my sons father sadly passed away when I was pregnant. I don’t like being alone so staying with my mom was the best since she’s a great person over all I see her more like my friend then my mom. The thing is I only have one sister I’m the oldest BUT she grabs EVERYTHING I have from clothes to even wasting my sons bath products. She will finish the food I buy with my own money and everything in general she will grab that’s mine or my sons. She’s homeschooled, doesn’t want to work. She’s so irresponsible and has a bad mouth. My mom won’t do much about it and I’m so fed up. I’m thinking of buying my own small fridge and putting the things I know she will eat in my room and finding a way to lock my room so she doesn’t go in there when I’m not home. This pisses me off because she doesn’t replace things. Also she will wear my brand new clothes and mess them up or stain them. And the worst is she denies things and I catch her always. My mom never grabs anything because she knows how I am that I don’t like even my son grabbing my belongings.

Am I over exaggerating or do I have the right to be upset?

P.s I’m moving in 3 months because of this reason. But I’m still on the hunt to find the perfect place. So that’s already one thing I will do but for the moment I need a solution.

Edit: I have told her SOOOO MANY TIMES. It has been to the point of us physically getting at each other. She’s so aggressive and snaps at everything but she doesn’t get it and continues to do it. That’s why now I hide all my stuff... it’s sad.